Phased array antennas, such as those used in spaceborne synthetic aperture radar, often require two operating frequencies sharing a common aperture. Such antennas may in some cases excite electromagnetic emission in multiple modes using a single resonator. These structures generally do not provide dual polarization and are often too large for use as elements in phased arrays without introducing grating lobes.
Some antennas have however used more than a single resonator, each emitting at a single frequency.
Kerr et al, in U.S. Pat. No. 4,060,810, issued Nov. 29, 1977 describes a metal patch antenna operating in the L-band, which surrounds a higher frequency X-band microstrip patch antenna. However this antenna does not provide an electronically steerable array. The antenna elements can only emit using a single polarization each. In addition, the antenna is larger than desirable.
Izadian, in U.S. Pat. No. 5,300,936 issued Apr. 5, 1994 describes a loop radiator surrounding planar patch radiators, the radiators emitting at L-band and S-band. The planar radiators emit using (single) circular polarization. The loop radiator can only emit using a single polarization.
However this antenna also does not provide an electronically steerable array. No means is described to cause the antenna elements to be able to emit plural frequencies, each at two polarizations. In addition, the antenna is larger than desirable.
Patin etal, in U.S. Pat. No. 5,001,493 describes arrays of square patch antennas each surrounded by a square annular antenna. The antenna operates at different frequencies. However no means is described to cause the antenna elements to be able to emit plural frequencies, each at dual polarizations.
Braun et al, in U.S. Pat. No. 5,160,936, issued Nov. 3, 1992, teaches an array of S-band cells surrounded by a ground plane. A slot in each array radiates in the UHF band. However no means is described to cause the antenna elements to be able to emit plural frequencies, each at two polarizations.
Lefeuvre et al, in U.S. Pat. No. 5,233,364, issued Aug. 3, 1993, teaches that dual polarized antenna elements of the same or different types may be contained in an array. However, the structure of the described antenna is complex, and due to its structural form the elements can be easily misspaced during a rough spacecraft launch and it is thus not ideally suitable for space applications. In addition the antenna is larger than is desirable.